Teletypewriter system



Oct. 25, 1938., J. A. DUNCAN 2,134,076

TELETYPEWRITER SYSTEM Filed Sept. 25, 1936 s sheets-sheet 1' I v I v v r [J It a a H v o I g I- Q \l w 2 W 0 b 80 a? I F a a IN VE N TOR 0ct.25, 1938. J. A. DUNCAN TELETYPEWRITER SYSTEM Filed Sept. 25, 1936 3 Sheets-Sheet 2 INVENTOR J. A. DUNCAN ArmR/vEy Oct. 25 1938.

J. A. DUNCAN TELETYPEWRITER SYSTEM Filed Sept. 25, 1936 3 Sheets-Sheet 3 l w 4, Q

INVENTOR J. A. DUNCAN ATTORNEY Patented a. 25,1938

UNITED STATES,

PATENT OFFICE TELETYPEWRITEB. SYSTEM Application September 25, 1936, Serial No; 102,578

10 Claims.

This invention relates to teletypewriter systems and, more particularly, to systems which include a teletypewriter having contacts for performing various functions. It is an object of this invention to mount contacts for performing various functions, in a teletypewriter to be operated by the teletypewriter mechanism in response to the transmission and reception of any or all upper case characters without hindering the printing functions of these characters.

It is also an object of this invention to open and close, by means of a central teletypewriter, telegraph lines leading from a teletypewriter oflice to other teletypewriter stations.

It is a further object of this invention to provide a central teletypewriter oflice with an improvide switching device for switching various circuits.

It is an additional object of this invention to enable a subscriber at a teletypewriter station to connect his teletypewriter through a teletypewriter central office to another teletypewriter-station-without the assistance of an operator at the central office thereby effecting a saving in operating time. f

It is a further object of this invention to enable subscribers having their lines connected together at a central oflice to disconnect the lines at the central office without the assistance of an operator at the central office, thereby effecting a further saving in operating time.

These and other objects of the invention are attained by means of a plurality of contact assemblies mounted in a teletypewriter at various predetermined positions. The contacts are adapted to be operated by the teletypewriter mechanism in response to certain. preassigned teletypewriter signals which may, if desired, be sent from other teletypewriter stations. In the preferred embodiment of the invention, the operation of the contacts serves to operate relays which operate and lock-up to perform any desired functions, such as switching telegraph circuits. Also in the preferred embodiment of the invention, the operation of a particular contact unlocks the switching relays and causes them to deenergize thereby restoring the system to its normal condition. If desired, these relays may be designed to perform 50 a variety of functions, such as switching on and off a teletypewriter motor at an outlying teletype-, writer station.

Most of the contact assemblies are adjustably mounted in the central teletypewriter near the tops of the pull bars and are designed to be opthe circuits through most of the contacts are connected in series with a control circuit which is normally open at the armature and contact of V a normally unenergized control relay.

This control relay is provided with an energizing circuit having a normally open contact connected in series with it and is also provided with a locking-up circuit having a normally open contact in series with it. The contact in the lockingup circuit is designed to be closed when the platen assembly of the teletypewriter is shifted to its upper case position, and the contact in the energizing circuit is momentarily closed by a pull bar in response to the reception by the central teletypewriter of a preassigned upper case code selection. The closing of both of these contacts permits energization of the control relay and also enables the control relay to lock -up over the circuit leading through the platen contact. Thus, the control relay remains operated and locked-up only as long as the platen assembly remains in its upper case position.

As soon as the platen assembly is shifted to its lower case position, the platen contact opens thereby opening the locking-up circuit of the control relay which becomes deenergized and releases its armatures. The release of one of the armatures of the control relay opens the control circuit and all of the contact circuits connected in series with it thereby discontinuing the functions of most of the contacts until the control circuit is closed again. Therefore, the operation of these switching contacts will be effective to perform their various switching functions only after the control circuit has been closed. Likewise,

\ their operation will be effective only as long as the platen assembly remains in its upper case position and will be rendered ineffective as soon as the platen assembly is shifted to its lower case position.

A modification of the invention is similar to' the structure just described except that it uses a normally closed pull bar contact instead of the normally open platen contact which is left free to be used to perform any other function that may be desired. With this modification, when the normally open pull bar contact is closed in response to the reception by the central teletypewriter of a preassigned code signal, the control relay will become energized and will operate its armatures. The operation of one of the armatures closes a circuit for the control relay to lock-up through the normally closed pull bar contact thereby rendering the operation of the various switching contacts effective to perform their intended functions.

After the desired switching functions have been accomplished, further operation of the switching contacts can be rendered inefiective by transmitting a second pro-assigned code signal which causes the selecting mechanism of the central teletypewriter to select a particular pull'bar. .Operation of this pull bar opens the normally closed contact which, in turn, opens the locking-up circuit of the control relay. Consequently, the con trol relay becomes deenergized .and releases its armatures thereby opening the control circuit common to the switching circuits. Operation of the switching contacts will now be ineffectiveto perform their intended functions until the preassigned code signal has been transmitted to energize the control relay for closing the control circuit.

These and other features of the invention will now be described in detail with reference to the drawings in which:

Figure 1 represents a teletypewriter central office and shows a schematic diagram in perspective of a teletypewriter provided with special contacts and .circuit connections leading to the switching relays and having its platen assembly inthe lower case position;

Fig. 2 shows the switching relays at the central office and the other teletypewriter stations to which the teletypewriter central office shown in Fig. 1 is connected; .and

Fig. 3, which is somewhat similar to Fig. 1, represents an alternative method of controlling the effectiveness of the switching contacts.

The teletypewriter T, shown in Fig. 1, is similar to the teletypewriter disclosed in Patent 1,745,633 granted February 4, 1930 to S. Morton et al. The disclosure of this Morton etal. patent is incorporated herein by reference as a part of this specification. However, the invention is not limited to this type of teletypewriter nor is it limited to the specific structure shown in the drawings which is a preferred embodiment of the invention and is shown and described in order to illustrate and explain the features and principles of operation of the invention.

For purposes of illustration, teletypewriter T is shown to be located at a teletypewriter central oflice, although it may be located at an ordinary subscriber's teletypewriter station if desired. Connected to this central ofilce by telegraph lines L1 to Le, inclusive, are the subscribers teletypewriter stations S1 to Sc, inclusive, each of which is provided with a teletypewriter T1 to Te, inclusive, and a teletypewriter motor M1 to M6, inclusive. Each of the motors M1 to Ms, inclusive, is operated by an individual power supply source '31 to Be, respectively. At stations S1, S2, S3, and

$5 the energizing circuits leading from the respective local power supply sources to the motors are opened and closed by manually operable switches A1. A2, A3, and A5, respectively, controlled by the local attendant at each station.

The energizing circuit of the motor M4 is normally open at the armature and contact A4 of the normally unoperated relay 43. This energizing circuit is adapted to be opened and closed by any control method that may be desired, such as the method described in Patent 1,913,431 granted June 13, 1933 to W. Daum. The disclosure of this Daum patent is incorporated herein by reference as a part of this specification. The energizing circuit of motor M6 is normally open at contact As of relay Rs located at the central ofllce. It is to be understood that these different motor control circuits may be varied as desired to meet the particular requirements of a given system and that they are shownhere for the purpose of illustrating the wide extent to which the invention may be applied. It should also be understood that the invention is capable of use with any other type of line circuits, such as duplex circuits.

The teletypewriter Tat the central office has a motor M which is operated by a power supply source B over an energizing circuit closed by a manually operable switch lever A. Motor M operates teletypewriter T by means of gears G1 and G2 which alternately raise and lower the printing bail [9 to operate the pull bars selected by the code bars which are actuated by the selecting .mechanism l8,' and is described in the Morton et al. patent.

Adjustably mounted in the upper part of teletypewriter T just above the tops of the pull bars are the assemblies for contacts C, C2, C3, C5, Cs. and Ca. Although these contact assemblies have been shown to be adjustably mounted, it isto be understood that this is merely one form of the invention and that the contact assemblies may be fixedly located by being drilled and tapped onto the frame of the teletypewriter T. All of these contacts are normally open except contact C which is normally closed. Contacts C, C2, C3, C5, C6, and C8 are designed to be operated in response to selections of pull bars l1, I2, l3, I5, l6, and 81,

In the preferred embodiment of the invention, 4

this preassigned signal is what is known as a bell signal which is a signal ordinarily designed to effect the ringing of a bell in the teletypewriter T. With the type of teletypewriter shown in Fig. 1, a bell signal is what is known as an upper case signal and, accordingly, requires that it be preceded by a figures shift signal. Furthermore, if a code signal corresponding to a bell signal should be sent while the platen assembly 52 is in its lower case position, the bell pull bar 81 would not be selected but, instead, another pull bar (not shown) would be selected. Since this other pull bar is not selected by any upper case signal, its associated type bar (not shown) is blank in the upper case.

In addition to contacts C, C2, C3, C5, C0, and Ca, the switching mechanism also includes the normally open contact C1 which is operated by the platen assembly in a manner described in detail hereinafter. The switching mechanism further includes the normally open contacts C1 and C4 which are designed to be operated by portions of the teletypewriter mechanism only in response to the reception by the receiving relay R. of certain upper case teletypewriter code signals. The manner of operating contacts C1 and C4 will be described hereinafter in connection with the description of the operation of the system as a whole.

Since all of the contacts mentioned above, except contacts C and Ca, have their circuits open at the right armature and contact of control relay 8|, their operation will be effective to perform forming any of their switching functions until desired.

In the operation of the system, let it be assumed that the subscriber at station S1 wishes to connect himself through the central office to the subscriber at station S3. The subscriber at station S1 normally has his switch A1 closed during business hours so that his motor M1 is energized by his local power supply source B1. Accordingly, the subscriber, by means of his teletypewriter T1, first transmits a figures shift signal out over line L1, conductor 20, line L2, through station S2, line L2, conductor 2 I, through the normally closed contacts of relay R2, conductor 22, through the normally closed contacts of relay R1, conductor 23, sending contacts 26, conductor I8, receiving relay R, conductor 8, outer left armature of the normally unoperated relay R4, and then to grounded battery 24. l

The figures shift signal transmitted over this path energizes the receiving relay R which operates the selecting mechanism 8 to select the figures pull bar 41 which is then elevated by the reciprocating bail l9. In rising, pull bar 4'! causes its extension 48 to elevate the left end of bell crank 49. This causes the right end of bell crank 49 to dip down thereby releasing latch 50. The release of latch 50 allows spring 5| to pull the platen assembly 52 forward. The forward movement of the platen assembly 52 pulls lever 28 forward sufficiently to remove slot 15 from the path of travel of extension 29 of the so-called blank pull bar l4. At the same time, the forward movement of the platen assembly 52 pushes down the right end of bell crank lever 49 to close contact C7 for a purpose to be explained hereinafter.

The subscriber at station S1 now transmits a permutationcode bell signal which causes the bell pull bar 81 to be selected by the code bars 80 for operation by the reciprocating bail l9. During the resulting-elevation of pull bar 81, the top of pull bar 81 will momentarily close contact Ca. This closes a path for current from grounded battery 82- to pass through the winding of control relay 8|, over conductor '83, through contact Cs, conductor 84, conductor 85, and then to ground 86. Before contact C8 opens, due to the restoration of pull bar 81 to its normal position, control relay 8| operates both its armatures, the right armature closing a path across conductors 42 and 44 for a purpose to be explained hereinafter. Relay 8| now locks-up over a circuit traced from battery 82, through the winding of relay 8|, over the operated left armature, conductor 88, through contact C7 (now closed), conductor 89, conductor 85, and then to ground 86.

erated due to this locking-up circuit which remains closed until contact C1 is opened by the platen assembly 52 returning to its lower case position as will be described hereinafter.

The subscriber at station S1 next transmits a' preassigned permutation code combination of significant current variations which in this preferred embodiment of the invention, is known as a blank signal. Upon being receivedat the cenoperates bothits armatures.

Consequently, when contact Ca now opens, relay 8| will remain op-- tral offlce, this particular upper case permutation ,code signal causes the selecting mechanism l8 to select the blank pull bar l4. Accordingly, the printing bail l9 elevates the blank pull bar l4 with the result that extension 29 of pull bar |4 engages with lever 28 and tilts it up. This elevates the left end of lever 38 and, consequently, lowers the right end of lever 38 thereby allowing spring 3| to pull down the left end of lever 32. As a result, the right end of lever 32 is raised and allows the spring contact C4 to close.

This closing is only momentarybecause pull bar- I4 is soon lowered by the reciprocating bail l9, and spring TI then pulls lever 28back into the position shown in the drawings.

It shouldbe noted that contact C4 can only be closed by this upper case blank signal because, whenthe platen assembly 52 is in its lower case position, slot I5 in lever 28 would then be positioned over extension 29 of the blank pull bar M as is shown in Fig. 1.- Elevation of pull bar |4 would then be futile to cause the closing of contact C4 because extension 29 would pass through slot 15 and would thus be unable to tilt lever 28.

The closing of contact C4 momentarily closes the energizing circuit of 'relay R4 from grounded battery 33 through the winding of relay R4, conductor 4, contact C4, conductor 9, conductor 42, over the operated right armature of relay 8|, conductor 44, conductor 36, and then'to ground 31. As a result, relay R4 becomes energized and Before contact C4 opens, relay R4 locks-up over' a circuit leading from grounded battery 33, through the winding of relay R4, inner left armature, conductor 34, conductor 1, thromrh the normally closed contact C,

conductor 35, conductor 36, and then to ground 31. At the same time, the communication circuit is switched from grounded battery 24 to the joining conductor 38 and then to conductor '39, out over line L6 to station S6, over line L6, conductor 40, line L3, and then to station S3. Since the subscriber at station S3 normally has his switch A: closed during business hours, his motor M3 will be energized at this time by his local power supply source B3.

Before communication begins, the pull bars of the teletypewriter T should be relieved of their switching functions to prepare them for performing their ordinary printing functions. To do this, a so-called letters shift code signal is transmitted for causing the selecting mechanism |8 of teletypewriter T to operate the code bars 88 to select pull bar 53. Upon being elevated by the reciprocating bail I9, pull bar 53 elevates its extension 54 which correspondingly elevates the left end of lever 55 thereby depressing the right end of lever 55. When the right end of lever 55 is depressed, it causes the left end of hell crank 55 to be correspondingly depressed thereby causing the topend of bell crank 56 to move backward to the rear of the teletypewriter T. This acts as a lever to pull back the platen assembly 52.

In'traveling to the rear of the teletypewriter T, the platen assembly 52 causes latch 50 to also move to the'rear of the teletypewriter T-withthe latched in its lower case position, as is shown' in Fig. 1, where it remains until a figures shift signal is received by relay R. At the same time,

in moving to the rear, latch 50 releases its pressure on bell crank lever 49 and allows the right end of lever 49 to move upward. This permits the spring contact C1 to open thereby opening the locking up circuit of relay 8| which consequently releases its armatures. The release of the right armature of relay 8| opens the control circuit to prevent further operation of the switching relays. However, the operation of relay R4 will not be discontinued because relay R4 is locked-up and will remain locked-up until contact C is opened.

Accordingly, the system isnow in condition for communication to take place between the subscriber at station Si and the subscriber at station S3. Significant current variations transmitted by the teletypewriter T1 will travel over line L1, conductor 20, line L2, through station S2, line L2, conductor 2|, conductor 22, conductor 23, sending contacts 26, conductor I0, receiving relay R, conductor 8, conductor 38, conductor 39, line Le, through station S6, line Ls, conductor 40, line L3, and then to station S3.

Since both stations S4 and S5 are disconnected from the communication circuit at the armatures of relays R1 and R2, respectively, neither teletypewriter T4 nor teletypewriter T5 will record the signals sent from teletypewriter T1 at this time. Teletypewriter Te will also not record these signals due to the fact that the energizing circuit for its motor M6 is open at contact As of relay Rs. However, with the system in the condition shown in the drawings, teletypewriter T2 will follow the signals transmitted by teletypewriter T1 because the energizing circuit for its motor M2 is closed at switch A2. If the subscriber at station S2 finds that the message heing transmitted from station S1 to station S3 is of no interest to him, he can open switch A2 thereby shutting down his motor'Mz with the result that his teletypewriter T2 will not now record the signals being transmitted.

Thus, the subscriber at station S1, which may be located at a remote point, has connected himself through the central office to the distant subscribers station S3 without any assistance from an operator at the central oflice. In other words,

'the'subscriber at station S1 has switched both his and the other subscriber's lines 8 and 39 from their terminations at batteries 24 and 25, respectively, to the joining conductor 38 thereby switching the line conductors 8 and 39 together. Consequently, a considerable saving in operating time is effected since the subscriber atstation S1 simply transmits a bell signal to efiect the operation of relay 8| and then transmits the upper case code combination assigned to select pull bar l4 which closes contact C4 to operate relay R4 which immediately switches the-two lines 8 and 39 together without any act by an operator at the central oriice. This saving in operating time is of importance in certain types of business where time is of the essence and promptness in putting calls through is essential.

When the subscribers at stations S1 and S3 have finished communicating with each other, either one of them may effect a disconnection of their lines 8 and 39 at the central ofilce by transmitting a preassigned telegraphic permutation code signal from either station S1 or station S3. This signal is received by the receiving relay R at the central ofllce which accordingly actuates the selecting mechanism |8 to operate the code bars to select pull bar Bail |9 then elevates pull bar 61 thereby momentarily opening the normally closed contact C. The opening of contact C opens the locking-up circuit of relay R4. Consequently, relay R4 releases its armatures and switches the line conductors 8 and 39 from the joining conductor 38 to batteries 24 and 25, respectively, thereby disconnecting stations S1 and S: from eachother and restoring the system to its normal condition. If desired,.the subscriber at station S2 may also effect this disconnection. Since this disconnection is accomplished by any of the connected subscribers without the assistance of an operator at the central oflice, a further saving in operating time is efiected.

The nature of the business of the subscriber at station S1 may be such that it would be desirable for him to send a message to both the subscriber at station S3 and the subscriber at station So (which may, for example, be an outlying station near the central office) and have the message recorded practically simultaneously by the teletypewriters I: and Te. To accomplish this conference connection, it is first necessary to start the teletypewriter motor Me at station Ss by energizing relay Re. Accordingly, the subscriber at station S1 transmits a figures shift signal for selecting the figures pull bar 41 to eifect the release of latch 50 which then allows the platen assembly 52 to be pulled forward by spring 5|. In moving forward, the platen assembly 52 carries latch 50 forward along the top edge of bell crank 49 thereby forcing down the right end of bell crank 49 to close contact C1 which will remain closed during the time that the platen assembly 52 remains in its upper case position.

The subscriber at station S1 next transmits a bell signal over line L1, conductor 20, line L2, through station ,Sz, line L2, conductor 2|, conductor 22, conductor 23, sending contacts 26, conductor I0, receiving relay R, conductor 8, and then to grounded battery 24. This bell signal effects the closing of contact Cs which enables control r'elay 8| to operate and lock-up in the manner described above. The subscriber at station S1 now transmits a preassigned combination of code impulses over the circuit traced above. This permutation code combination causes the selecting mechanism |8 of teletypewriter T to select pull bar l6 which is then momentarily operated by the printing bail l9 to close contact Ca momentarily. A path for energizing relay Re is now closed from grounded battery 4|, through the winding of relay Rs, conductor 6, through contact Cc, conductor I8, conductor 42, over the operated right armature of relay 8|, conductor 44, conductor 36, and then to ground 31.

As a result, relay Rs operates its armatures and locks-up through a path from battery 4|, through the winding of relay Rs, operated left armature, conductor 34, conductor 1, through the normally closed contact C, conductor 35, conductor 38, and then to ground 31. At the same time, the right armature of relay Re is operated and closes a path from power supply source B6 at station So. over llnevconductor 45, operated armature and contact As of relay Re, line conductor 46, motor Ma, and then back to power supply source Ba on both the teletypewriters T3 and T6.

relays are locked-up through the normally closed contact C.

Messages now sent from station S1 will pass through station S2, through the central oflice, and then through stations Se and S3. The messages will thus be recorded practically simultaneously They will also be recorded on the teletypewriter T2 at station S2 provided the subscriber at this station has his switch A: closed. The subscriber at station S3 can transmit messages to any of the connected stations and these messages will be practically simultaneously recorded by the teletypewriters T1, T2 and Te. Likewise, the subscriber at station Se can also send messages which will be recorded on all of the connected teletypewriters.

At the close of communication, any of the subscribers at stations S1, S2, S3, or 56 may disconnect the conference connection by transmitting the preassigned code signal for selecting pull bar I! which will momentarily open the normally closed contact C as was described above. The opening of contact C will open the locking-up circuits of both relays R4 and R5 and will cause them to release their armatures. This switches thecommunication circuit from conductors 8 and 39 to batteries 24 and 25 as was described above. At the same time, the energizing circuit of motor Me is opened at contact As of relay Re and, consequently, motor Me stops running. The system is thus restored to its normal condition.

In the event that the subscriber at station S1 wishes to communicate with the subscriber at v station S4 (which may, for example, be an outlying station near the central oflice), he will transmit the figures shift signal to cause the platen 21 to be shifted to its upper case position. The subscriber will then transmit a preassigned upper case code signal which, upon being received by the receiving relay R, will effect the selection of pull bar II by the-selecting mechanism I8 and the code bars 89. The elevation of pull bar I! by reciprocating bail [9 will, by means of ratchet 57 and gear 58,.drive the top of type bar 59 downward in an arcuate path. I

The projection 90 on bar 59 will then hit lever 60, thereby tilting downward the right end of lever 6!. This drives the top end of lever to the right and allows spring 62 to pull down the right end'of lever 63 into latching engagement with the top end of lever 6|. Consequently,-the left end of lever 63, which is normally located immediately beneath the printing bail l9, as shown in the drawings, is driven upward to close contact C1 momentarily. It should be noted that contact C1 can only be closed by an upper case selection of pull bar ll because, when the platen assembly 52 is in its lower case position, lever 60 is carried to the rear of teletypewriter T a short distance which is sufllcient to remove it from the path of travel of projection 90.

The closure of contact C1 closes a path from grounded battery 64, through the winding of relay R1, along conductor I. through contact C1,

conductor 65, conductor 42, operated right armature of relay 8|, conductor 44, condllGtor 36, and

then to ground 31. Consequently, relay R1 operates its armatures and locks-up through its right armature over a path from grounded batmature and contact of relay R1, conductor 34, conductor I, normally closed contact C, conductor 35, conductor 36,'and then to ground 31. It is necessary that relay R1 be designed to lock-up quickly because, when the reciprocating bail l9 comes down, it forces down the left end of lever.

v tery 64, winding of relay R1, operated. right ar- 63, thereby permitting contact C1 to resume its normally open position. At the same time, the right end of lever 63 is forced upward thereby allowing spring I0! to pull back the top end of lever 6| into the lower notch in the right end of lever 63 as is shown in the drawings.

The operation of the two left armatures of relay R1 opens the normally closed make-beforebreak left contacts of relay R1 and closes a path from conductor 22, over the inner left armature of relay R1, conductor 66, line L4, through station Saback over line L4, conductor 61, outer left armature of relay R1; conductor 23, sending contacts 26, conductor l0, relay R, conductor 8, and then to grounded battery 24. The subscriber at station S1 now transmits motor start signals, such 'as those described in the Daum patent mentioned above, which efiect the energization of a relay 43 at station S4, similar to the motor control relay disclosed in the Daum patent. Upon being energized, motor control relay 43 operates its armature to close the contact A4, thereby closing the energizing circuit of motor M4 and starting motor. M4 into operation.

After opening the control circuit in the manner described above to relieve the pull bars of their switching Simctions, communication may now take place between stations S1, S2, and S4, the'signals passing out over line L1, conductor 20, line L2, through station S2, line L2, conductor 2!, conductor 22, conductor 66, line L4, through station S4, line L4, conductor 61, conductor 23, and

then to grounded battery 24 as was described above. These signals will also pass through the receiving relay R. It might be mentioned here that this is the case with all connections between the various subscribers stations; that is, receiving relay R follows all the signals sent between these stations.

At the close of communication, any of the subscribers at the three connected stations S1, S2,

station- S4 andconnect conductor 22 directly to conductor 23. Incidentally, the motor at station S4 may be stopped by any of the subscribers in the manner described in the Daum patent. It might be stated here that, in this embodiment of the invention, the central office operator can effect any of the connections and disconnections between any of the subscribers stations because her sending contacts 26 are always connected in 1 series with the communication circuits. This circuit construction can be modified in accordance with the requirements of different systems.

If the subscriber at station S1 wishes to send a message to be recorded by the teletypewriters T3 and T4 at stations S3 and S4 (leaving station S2 out of consideration for the sake of simplicity), he will, after first transmitting a bell signal to operate relay ill, send the code signals to select pull bars I I and I4 for closing contacts C1 and C4. This will operate relays R1 and R4 which will lock-up as described above to close the lines leading to stations S5 and S4. Any of the connected subscribers may disconnect this Conference connection by sending the code signal to select pull bar l1 for opening contact C. This opens the locking-up circuits of both relays R1 and R4, thereby restoring the system to its normal condition.

Also, if the subscriber at station S1 wishes to send a message to be recorded by the teletyp'ewriters at each of the stations S3, S4, and S6 (again leaving station S2 out of consideration. for the sake of simplification), he will follow the same procedure as that outlined in the preceding paragraph except that he will, in addition, send the code signal to select pull bar IS. The operation of. pull bar IE will close contact C6 and operate relay Re which will lock-up and close the energizing circuit of motor Me at station Se, thereby conditioning station So for the reception and transmission of messages. Any of the connected subscribers, or the central .oifice operator, may disconnect this conference connection in the manner described above.

Likewise, the subscriber at station S1 may connect himself through the central ofiice to the station S5 by transmitting a bell signal (thereby operating control relay 8| which locks-up as described above) followed by the preassigned code combination for selecting pull bar l2. The elevation of pull bar l2 by bail l9 momentarily closes contact C: thus closing the energizing path for relay R; from grounded battery 68, through the winding of relay R2, conductor 2, contact C2, conductor 99, conductor 42, over the operated 'right armature of relay 8|, conductor 44, conductor 36, and then to ground 31 thereby energizing relay R2.

Upon being energized, relay R2 operates its armatures and locks-up from battery 68, through the winding of relay R2, operated left armature, conductor 34, conductor 1, through the normally closed contact C, conductor 35, conductor 36, and. thento ground 31. In operating its two right armatures, relay R: switches the line circuit from along conductor 2!, over the outer right operated armature of relay R, conductor 69, line Ls, teletypewriter T5 at station S5, back over line L5, conductor 10, inner operated right armature of relay R2, conductor 22, conductor 23, and then zhroifih the receiving relay R, to grounded batery If a conference connection is desired, other stations may be connected into the communica tion circuit in the manner described above. At

, the close of communication, any of the connected subscribers may disconnect the connection by effecting the operation, or opening, of the normally closed contact C at the central oiiice by causing the operation of pull bar l1 as described J above.

and then the preassigned The operation of pull bar right armature of control relay 8|, conductor 44, conductor 36, and then to ground 31 thereby energizing relay R3. Upon being energized, relay R3 operates its armatures and locks-up over a path from grounded battery 1|, through the winding of relay R3, operated left armature, conductor 34, conductor 1, through the normally closed contact C, conductor 35, conductor 36, and then to ground 31. In operating its right armatures, relay R3 will perform the desired switching function.

When it is desired to discontinue the switching operation, the upper case code signal is sent for causing pull bar l1 to open the normally closed contact C which opens the locking-up circuit of relay R5 thereby causing relay R3 to release, thus restoring the system to its normal condition.

If. it is desired to perform still another switching function, it may be effected by sending a bell signal to operate contact Ca for operating relay 8| and then transmitting the preassigned upper case code combination for selecting pull bar IS. The elevation of pull bar l5 momentarily operates the switching contact C5 for closing a path from grounded battery 13, through the winding of relay R5, conductor 5, contact C5, conductor 14, conductor 42, over the operated right armatureofrelay 8|, conductor 44, conductor 36, and then to ground 31 thereby energizing relay R5. Upon operating its armatures, relay R5 will lockup over a path leading from grounded battery 13, through the winding of relay R5, operated left armature, conductor 34, conductor 1, through the normally closed contact C, conductor 35, conductor 36, and then to ground 31. In operating its right armatures, relay R5 will perform the desired switching functions.

When it is desired to terminatethis switching operation, the upper case signal for effecting the opening of the normally closed contact is transmitted thereby opening the locking-up circuit of relay R which now releases its armatures and restores the system to its normally unoperated condition.

If additional operations, or functions, are desired, more contacts can be mounted in the teletypewriter T and can be connected into the system in a manner similar to that in which the other contacts are connected.

Whereas the operation of the system has been described principally with reference to connections originating from the dominant station Si, it is to be understood that the connections described above may be eifected and disconnected in a similar manner by the subscriber at the other dominant station S2. It is to be further understood that other dominant stations may be added according to the particular requirements of an individual system.

For the purpose of illustration, contact C1 has been shown to be operable by an individual arrang'ement of the teletypewriter apparatus. If

it is desired to have levers 60, 6| and '63 perform some other function, contact C1 may be mounted above a pull bar the same as contacts C2, C3, C5, and C6. The same applies to contact C4, which has also been shown to be operable by an individual arrangement of the teletypewriter apparatus. If it is desired to have levers 28, 30, and 32 perform some other function, this may readily be accomplished by placing contact C4 above a pull bar the same as contacts C2, C5, C5, and Cs. Contact C may be arranged to be operated in reerable to design the selecting mechanism of teletypewriter T in such a manner that pull bar |1 will only be selected in response to an upper case selection.

Thus, by means of this invention, all the various pull bars (except bar l1) of the teletypewriter T at the central oiiice may be used for performing relay 8| is unenergized. This is due to the fact.

that, if the control circuit were not open at the contact and unoperated right armature of control relay 8|, every time the pull bars should be operated, they would close their contactsfor energizing the particular switching relays associated therewith.

Itis to be understood that this specific application of the invention has been shown and described for purposes of explaining the principles and features of operation of the, invention. Changes may be made in the construction shown without exceeding the scope of the invention. More switchingcontacts to be operated by the pull bars of the teletypewriter at the'central ofllce may be added whenever desired to perform any functions that may be required. Likewise, the

circuit connections of the various subscribers stations may be varied as desired to meet the requirements of any particular communication system.

A modification of the invention is shown in Fig. 3 which'discloses a central ofllce teletypewriter equipped with switching contacts somewhat similar to those disclosed in Fig. 1 and having circuits leading to the switching relays and subscribers stations shown in Fig. 2. The de vice shown in Fig. 3 difiers from that shown in Fig. 1 in that control relay 9| is used instead of control relay 8|. Furthermore, the effectiveness of most of the contacts is controlled by the control relay 9|. Relay 9| is designed to operate and lock-up in response to a particular permutation code signal which efi'ects the-closing of a normally open contact C9 and is designed to unlock in response to another preassigned permutation code signal which eifects the opening of the lockingup circuit through the normally closed contact C10. With this modification, before the operation of contacts C1, C2, C3, C4, C5, and Co will be effective to perform any useful switching functions, their operating circuits must be closed. It can be seen in Fig. 3 that each of their operating circuits is open, not only at the particular normally open contacts, but also at the unoperated right armature and contact of relay 9|. Consequently, when it is desired to perform the switching function controlled by'one of these contacts, the preassigned code signal is sent to operate the selecting 'mechanism |8 which actuates the code bars 89 to select pull bar 92. When pull bar 92 is elevated by the printing bail |9,'the top of bar 92 will momentarily close contact C9.

The closure of contact C9 closes a path for operating control relay 9| from' grounded battery 93, through the winding of relay 9|, conductor 94, contact C9, conductor 91,conductor 39, and

then to ground 31. Consequently, control relay 9| becomes energized and operates its armatures. The operation of the left armature of relay 9| closes a locking-up circuit for relay 9| which accordingly locks-up over a circuit traced from grounded battery 93, through the winding of relay 9 I, operated left armature of relay 9 I, through the normally closed contact Cm, conductor 95, conductor 91, conductor 36, and then to ground 31. Consequently, control relay 9| remains operated until its locking-up circuit is opened in response to the preassigned code signal for selecting pull bar 96 to open the normally closed contact At the same time, the operation of the right armature of relay 9| .closes a path from conductor 98 (which is common to each of the con- In other words, the operation of the right armature of relay 9| applies ground 31 to each of contacts C1, C2, C3, C4, C5, and C6. Thus, the code signals for operating each of these contacts must be preceded by'the preassigned code signal for closing contact C9 to operate control relay 9| or the operation of the contacts will be ineffective to accomplish any useful function.

For example, if the subscriber at station S1 should wish to connect his station-S1 to station S5, he would first transmit the preassigned signal for tacts C1, C2, C3,-C4, C5, and C6) to conductor 91.

selecting pull bar 92. The elevation of pull bar 92 by bail l9 would momentarily close contact Ca thereby closing the path traced above for operating relay 9| which would lock-up in the manner described above. Then the permutation code signal for selecting pull bar l3. would be sent to elevate pull bar l3 thereby closing contact C3. This would operate relay R3 over a path traced from grounded battery 1 through the winding of relay R3, conductor 3, contact Ca, conductor 12;, conductor 99, over the operated right armature of relay 9|, conductor 91, conductor 36 and then to ground 31. Relay R3 would then lock-up over a circuit leading from battery 1|, through the Windingv of relay R3, operated left armature of relay R3, conductor 35, conductor 1, through the normally closed contact C, conductor 35, conductor 36, then to ground 31.

If it is desired to add any other stations to the communication circuit at this time, the signal for selecting the pull bar l3 may be immediately followed by the preassigned permutation code signals for selecting pull bars l2, l5, or any other desired contact operating pull bar. Then, when all of the desired stations have been added to the communication circuit, the preassigned code signal is sent for effecting the selection of pull bar 96. The elevation of pull bar 96 by bail i9 opens the normally closed contact C10 thereby opening the locking-up circuit of relay- 9| which, conse-' quently, releases both its armatures. This removes ground 31 from the switching contacts and relieves most of the contact operating pull bars from their switching functions. Since pull bars l2, l3, l4, l5, l5, and 96 may now be used for performing their ordinary printing functions, communication may take place. I At the close of communication, the permutation code signal is sent for selecting pull bar H. The operation of contact C by the elevation of pull bar i1 opens the normally closed contact C which opens the locking-up circuits of the switching relays thereby restoring the communication systern to its normal condition.

sired. Contact C7 is shown to be bridged across the conductors 42 and 44 which may lead to the desired switching apparatus. The movement of the platen assembly 52 from its lower case position (shown in Fig. 3) to its upper case position closes contact C7 in the manner described above. Likewise, the movement of the platen assembly 52 from its upper case position to its lower case position opens contact C1. The particular switching function to be accomplished by contact C1 may be any function convenient to the requirements of a particular communication system.

It is to be understood that the circuits shown in Z the drawings are presented for purposes of illustration and it is to be further understood that they may be modified as desired. For example, the teletypewriter at each subscribers station may be provided with switching contacts so that it will connect and disconnect telegraph lines. After the lines have been connected, the subscriber 'may relieve the pull bars in his teletypewriter of their switching functions and proceed with ordinary communication since the pull bars of this teletypewriter can then be used for performing only their ordinary upper and lower case printing functions.

What is claimed is:

1. A teletypewriter system including a teletypewriter having pull bars, selecting mechanism operable in response to the reception by the teletypewriterof preassigned code combinations of signal impulses for selecting the pull bars, a reciprocating bail for elevating the pull bars selected by the selecting mechanism, switching contacts mounted'in the teletypewriter for operation by the pull bars when the pull bars are elevated, circuits adapted to be opened and closed by the switching contacts, theoperaticn of said contacts being normally .ineifective to perform any useful function, and control means for rendering the operation of said pull bar operated switching contacts effective, said control means including a normally unenergized relay operable only in response to the reception by the teletypewriter of a preassigned code combination of signal impulses.

2. A teletypewriter system including a teletypewriter having pull bars, selecting mechanism for selecting certain of the pull bars, a reciprocating bail for elevating the pull bars selected by the selecting mechanism, switching contacts mounted in the teletypewriter for operation by the pull bars when the pull bars are elevated, circuits adapted to be opened and closed by the switching contacts, the operation of said contacts being normallyineifective, and control means for rendering the operation of said switching contacts effective, said control means including a normally unenergized relay having a normally open energizing circuit and a normally open locking-up circuit, a first normally open control contact connected in series with the energizing circuit, a second nor?- mally open control contact connected in series with the locking-up circuit, a first instrumentality for closing the first control contact to close the energizing circuit, and a second instrumentality for closing the second control contact to close the locking-up circuit.

3. A teletypewriter system including a teletypewriter having pull bars, selecting mechanism for selecting certain of the pull bars, a reciprocating bail for elevating the pull bars selected by the selecting mechanism, switching contacts mounted in the teletypewriter for operation by the pull bars when. the pull bars are elevated, circuits adapted to be opened and closed by the switching contacts, the operation of said contacts being normally ineffective, and control means for rendering the operation of said switching contacts effective, said control means including a normally unenergized relay having a normally open energizing circuit and a normally open locking-up circuit, means for closing the locking-up circuit, a normally open control contact connected in series with the energizing circuit, a normally closed control contact connected in series with the locking-up circuit, a first instrumentality for closing the normally open control contact to energize the control relay, and a second instrumentality for opening the normally closed control contact to open the locking-up circuit of the control relay.

4. A teletypewriter having a plurality of pull bars, selecting mechanism for selecting certain of the pull bars, a reciprocating bail for elevating the pull bars selected by the selecting mechanism, switching contacts mounted in the teletypewriter for operation by the pull bars when the pull bars are elevated, circuits, adapted to be opened and closed by the switching contacts, a normallyopen contact connected in series with said circuits whereby the operation of said contacts is normally inefiective to perform any useful function, a relay adapted to close the normally open contact for rendering the operation of the switching contacts effective, and operating means for energizing the relay.

5. A teletypewriter having shift mechanism, a

plurality of pull bars, selecting mechanism for selecting certain of the pull bars, a reciprocating bail for operating those pull bars selected by plurality of pull bars, selecting mechanism for selecting certain of the pull bars, a reciprocating bail for elevating those pull bars selected by the selecting mechanism, contacts mounted in the teletypewriter for operation by the pull bars when the pull bars are elevated, circuits adapted to be opened and closed by the contacts, a normally open contact connected in series with said circuits, and electroresponsive means for closing and opening the contact, said electroresponsive means being energized in response to the reception by the teletypewriter of a preassigned code signal and being deenergized in response to the reception of a different preassigned code signal.

'7. A teletypewriter including in combination aplurality of pull bars, selecting mechanism for selecting certain of the pull bars, a reciprocating bail for elevating those pull bars selected by the selecting mechanism, contacts mounted in the teletypewriter for operation by the pull bars when the pull bars are elevated, circuits adapted to be opened and closed by the contacts, a control circuit connected in series with each of said circuits, a normally unenergized control relay havin-ga normally open armature contact, said control circuit being normally 'open at said normally open armature contact, and control means for energizing and deenergizing the control relay,

said control means including a normally open contact.

8. A teletypewriter system having in combination a teletypewriter central oflice with a. teletypewriter, a plurality of telegraph'lines, a plurality of teletypewriter stations connectable to the central office by the telegraph lines and normally disconnected from each other, instrumentalities for enabling an operator at one of the teletypewriter stations to connect himself through the central office to one of the'other teletypewriter stations, said instrumentalities including a control relay at the central oflice connected in series with said instrumentalities, and means for energizing the control relay only in response to the reception of a preassigned code signal that has been preceded by a difierent preasslgned code signal.

9. A teletypewriter system having a teletypewriter central ofilce with a teletypewriter having a plurality of pull bars, a plurality of teletypewriter stations connected to the central office by a plurality of telegraph lines, normally unoperated switching apparatus at the central.

'office operable in response to certain pre'assigned code signals for switching said telegraph lines,

and a control relay at the central oflice for rendering the operation of the switching apparatus a connecting the teletypewriter stations to the central office, normally unoperated switching appa ratus at the central oflice operable in response to certain preassigned code signals for switching said telegraph lines, a control relay for rendering the operation of the switching apparatus ineffective to perform any useful function, means for energizing the control relay in response to the operation of one of the pull bars, and means for deenerglzing the control relay in response to the operation of a different pull bar.

JAMES ARCHIBALD DUNCAN. 

